This invention claims priority of the German patent application 100 30 013.8 and 101 15 589.1 which are incorporated by reference herein.
The invention relates to an illuminating device having a laser that emits a light beam, which is directed onto a microstructured optical element that spectrally broadens the light from the laser.
Laid-open patent specification DE 198 53 669 A1 discloses an ultrashort-pulse source with controllable multiple-wavelength output, which is used especially in a multiphoton microscope. The system has an ultrashort-pulse laser for producing ultrashort optical pulses of a fixed wavelength and at least one wavelength conversion channel.
U.S. Pat. No. 6,097,870 discloses an arrangement for generating a broadband spectrum in the visible and infrared spectral range. The arrangement is based on a microstructured fibre, into which the light from a pump laser is injected. The pump light is broadened in the microstructured fibre by non-linear effects. So-called photonic band gap material or xe2x80x9cphotonic crystal fibresxe2x80x9d, xe2x80x9choley fibresxe2x80x9d or xe2x80x9cmicrostructured fibresxe2x80x9d are also employed as microstructured fibres. Configurations as a so-called xe2x80x9chollow fibrexe2x80x9d are also known.
Another arrangement for generating a broadband spectrum is disclosed in the publication by Birks et al.: xe2x80x9cSupercontinuum generation in tapered fibresxe2x80x9d, Opt. Lett. Vol. 25, p.1415 (2000). A conventional optical fibre having a fibre core, which has a taper at least along a subsection, is used in the arrangement. Optical fibres of this type are known as so-called xe2x80x9ctapered fibresxe2x80x9d.
An optical amplifier, whose gain can be adjusted as a function of the wavelength, is known from the PCT application with the publication number WO 00/04613. The said publication also discloses a fibre light source based on this principle.
Arc lamps are known as broadband light sources, and are employed in many areas. One example is the U.S. Pat. No. 3,720,822 xe2x80x9cXENON PHOTOGRAPHY LIGHTxe2x80x9d, which discloses a xenon arc lamp for illumination in photography.
Especially in microscopy, universal illuminating devices with high luminance are important for the illumination of microscopic preparations. In scanning microscopy, a sample is scanned with a light beam. To that end, lasers are often used as the light source. For example, an arrangement having a single laser which emits several laser lines is known from EP 0 495 930: xe2x80x9cKonfokales Mikroskopsystem fxc3xcr Mehrfarbenfluoreszenzxe2x80x9d [confocal microscope system for multicolour fluorescence]. Mixed gas lasers, especially ArKr lasers, are mainly used for this at present. Examples of samples which are studied include biological tissue or sections prepared with fluorescent dyes. In the field of material study, illumination light reflected from the sample is often detected. Solid-state lasers and dye lasers, as well as fibre lasers and optical parametric oscillators (OPOs), upstream of which a pump laser is arranged, are also frequently used.
The illuminating devices known from the prior art have several disadvantages. The known broadband illuminating devices mostly have a low luminance compared with laser-based illuminating devices, whereas the latter provide the user only with discrete wavelength lines whose spectral position and width can be adjusted only to a small extent, if at all. Owing to this limitation of the working spectrum, the known illuminating devices are not flexibly usable.
By using microstructured fibres, as described in the previously mentioned U.S. Pat. No. 6,097,870, a broad continuous wavelength spectrum is accessible. Arrangements of the disclosed type, however, are difficult to handle, inflexible and susceptible to interference, especially because of the complexity of the individual optical components and their relative adjustment.
It is an object of the invention to provide an illuminating device which is easy to handle, reliable, flexible and not susceptible to interference.
The object is achieved by an illuminating device comprising: a laser that emits a light beam, a microstructured optical element on which the light beam is directed and wherein the microstructured optical element spectrally broadens the light beam and a casing, defining an exit opening from which the spectrally broadened light beam emerges and wherein the laser and the microstructured optical element are arranged within the casing.
A further object of the invention is to create microscope with an illumination device for illuminating a preparation which provides an illumination encompassing a numerous selectable spectral regions.
The aforesaid object is achieved by a microscope comprising: an illuminating device for illuminating a preparation having a laser that emits a light beam and a microstructured optical element on which the light beam is directed, wherein the microstructured optical element spectrally broadens the light beam.
The invention has the advantage that it is universally usable, easy to handle and flexible, and furthermore provides light from a wide wavelength range.
In a preferred configuration, the illuminating device has a casing with a light exit opening, from which the spectrally broadened light emerges. This has the advantage that, in particular, the optical components are protected against external effects and especially against dirt.
A configuration variant in which a lens, which shapes the spectrally broadened light into a beam, is arranged downstream of the microstructured optical element, is especially advantageous. This lens is preferably located inside the casing, immediately in front of the light exit opening. With regard to beam safety, a warning light preferably fitted to the casing, which indicates the activity of the illuminating device to the user, is provided.
All common laser types may be used as the laser. In a preferred configuration, the laser is a short-pulse laser, for example a mode-coupled or mode-locked solid-state laser, which emits light pulses with a period of from 100 fs to 10 ps.
An embodiment of the illuminating device which contains an instrument for varying the power of the spectrally broadened light is especially preferred. In this case, it is more particularly advantageous to configure the illuminating device in such a way that the power of the spectrally broadened light can be varied or can be fully stopped-out with respect to at least one selectable wavelength or at least one selectable wavelength range.
Acousto-optical or electro-optical elements, such as e.g. acousto-optical tunable filters (AOTFs), are preferably usable as the instrument for varying the power of the spectrally broadened light. It is likewise possible to use dielectric filters or colour filters, which are preferably arranged in cascade. Particular flexibility is achieved if the filters are fitted in revolvers or in slide mounts, which allow easy insertion into the beam path of the spectrally broadened light.
In another configuration, provision is made for the spectrally broadened light to be spectrally resolved in a spatial fashion, in order to make it possible to suppress or fully stop-out spectral components with a suitable variable aperture arrangement or filter arrangement, and subsequently recombine the remaining spectral components to form a beam. A prism or a grating, for example, may be used for the spatial spectral resolution.
To vary the power of the spectrally broadened light, in another alternative embodiment, a Fabry-Perot filter is provided. LCD filters can also be used.
An embodiment which has, directly on the casing, operating elements for adjusting the light power and the spectral composition of the spectrally broadened light, is especially advantageous. In another embodiment, these parameters are adjusted on an external control panel or on a PC, and the adjustment data is transmitted in the form of electrical signals to the illuminating device, or to the instrument for varying the power of the spectrally broadened light. Adjustment using sliders, which are shown on a display and, for example, can be operated using a computer mouse, is particularly clear.
According to the invention, it has been discovered that the divergence and the diameter of the light beam, which is emitted by the laser and is directed onto the microstructured optical element, has a considerable influence on the spectral distribution within the spectrally broadened light. In a particularly preferred and flexible configuration, the illuminating device contains a focusing lens which focuses the light beam from the laser onto the microstructured optical element. Embodiment of the focusing lens as a variable lens, for example as a zoom lens, is particularly advantageous.
In the illuminating device, an instrument is preferably provided which permits analysis of the broadened-wavelength light, in particular with regard to the spectral composition and the luminance. The analysis instrument is arranged in such a way that part of the spectrally broadened light is split off, for example with the aid of a beam splitter, and fed to the analysis instrument. The analysis instrument is preferably a spectrometer. It contains, for example, a prism or a grating for the spatial spectral resolution, and a CCD element or a multichannel photomultiplier as the detector. In another variant, the analysis instrument contains a multiband detector. Semiconductor spectrometers can also be employed.
To establish the power of the spectrally broadened light, the detectors are configured in such a way that an electrical signal, which is proportional to the light power and can be evaluated by electronics or a computer, is generated.
The embodiment which contains a display for the power of the spectrally broadened light and/or for the spectral composition of the spectrally broadened light is more particularly advantageous. The display is preferably fitted directly on the casing or to the control panel. In another embodiment, the monitor of a PC is used for displaying the power and/or the spectral composition.
In a preferred configuration of the scanning microscope, the microstructured optical element is constructed from a plurality of micro-optical structure elements, which have at least two different optical densities. A configuration in which the optical element contains a first region and a second region, the first region having a homogeneous structure and a microstructure comprising micro-optical structure elements being formed in the second region, is more particularly preferred. It is furthermore advantageous if the first region encloses the second region. The micro-optical structure elements are preferably cannulas, webs, honeycombs, tubes or cavities.
In another configuration, the microstructured optical element consists of adjacent glass or plastic material and cavities. A particularly preferred alternative embodiment is one in which the microstructured optical element consists of photonic band gap material and is configured as an optical fibre, an optical diode, which suppresses back-reflection of the light beam from the laser due to the ends of the optical fibre, being preferably arranged between the laser and the optical fibre.
A more particularly preferred alternative embodiment, which is simple to implement, contains a conventional optical fibre having a fibre core diameter of approximately 9 xcexcm, which has a taper at least along a subsection, as the microstructured optical element. Optical fibres of this type are known as so-called xe2x80x9ctapered fibresxe2x80x9d. The optical fibre preferably has an overall length of 1 m and a taper over a length of from 30 mm to 90 mm. The diameter of the optical fibre, in a preferred configuration, is approximately 2 xe2x96xa1m in the region of the taper. The fibre core diameter is correspondingly in the nanometer range.
The illuminating device can be used more particularly for the illumination of a microscopic sample, especially in a scanning microscope or a confocal scanning microscope.